Radiation-induced lung injury is a significant side effect of radiation therapy for many lung cancer patients. Although higher radiation doses increase the radiation therapy effectiveness for tumor control, such higher doses may lead to lung injury because, under such conditions, a greater quantity of normal lung tissue may be included in treated areas. In recent studies, nearly 40% of patients who underwent radiation therapy developed lung injuries following treatment. Lung injury may take the form of acute radiation pneumonitis occurring less than six months after treatment, or lung injury may take the form of lung fibrosis, happening after six months of treatment. Conventional approaches to the detection and characterization of radiation-induced lung injury are expensive and rely on slow machines that produce images that have insufficient resolution.
Early detection may help to improve management of the treatment of radiation-induced lung injury. Conventional approaches that rely only on the appearance of computed tomography (CT) scans (i.e., Hounsfield Units) do not enable early detection of radiation-induced lung injury, making treatment more difficult. Alternatively, detection of early radiation-induced lung injury development through monitoring of lung functionality and lung texture changes may substantially improve the disease management. Although global pulmonary function tests (PFT), such as spirometry, measure air flow obstruction/restriction, no regional lung function information is obtained. Alternatively, the lung functionality may be locally evaluated using nuclear imaging, e.g., by single-photon emission computed tomography (SPECT) ventilation and perfusion (V/Q) images. However, SPECT image acquisition is highly expensive and relies on relatively slow machines, which produce images having insufficient spatial resolution.
Recently, four-dimensional computed tomography (4D-CT) scans have gained attention for assessing lung functionality in that such sans provide high spatial resolution, faster acquisition, and relatively low cost. Moreover, in addition to texture, many functional features may be derived from 4D-CT scans. The lung ventilation may be derived from the 4D-CT scans and these results may be correlated with the SPECT (V/Q) scans, or the ventilation maps may be correlated directly with certain clinical findings.
Despite limited success, however, conventional methods for detecting radiation therapy effects have several significant limitations. Global PFTs measure total airflow but fail to provide information about regional functionality. Nuclear imaging based detection of defects in local pulmonary function, for example, suffers from low spatial resolution. Conventional voxel-wise descriptors of lung appearance are too sensitive to noise and fail to take account of dependences between adjacent voxels to suppress noise impacts. Further, common computational models for aligning the 4D-CT images do not guarantee proper voxel-to-voxel matches, often leading to inaccurate estimates of lung functionality parameters.